U.S. patent application number 09/897389 was filed with the patent office on 2002-01-10 for optical demultiplexer/multiplexer.
Invention is credited to Jinnai, Kuniaki, Takano, Toshihiko.
Application Number | 20020003922 09/897389 |
Document ID | / |
Family ID | 18699795 |
Filed Date | 2002-01-10 |
United States Patent
Application |
20020003922 |
Kind Code |
A1 |
Takano, Toshihiko ; et
al. |
January 10, 2002 |
Optical demultiplexer/multiplexer
Abstract
An optical demultiplexer/multiplexer, obtained by improving a
conventional optical demultiplexer/multiplexer comprising a filter
unit in which plural selective transmission/reflection optical
filters (F(k)) are disposed on a plane A and a plane B arranged in
parallel, an external light input/output port (E (0)) disposed
outside the filter unit and positioned on the reflecting light axis
of F(1) and plural light input/output ports (P (k)) disposed on the
transmission light axes of F(k) and on the reflecting light axis of
F(n-2), provided that n is an integer of 4.ltoreq.n.ltoreq.9,
wherein the improvement is comprising a selective
transmission/reflection optical filter (F0) which transmits lights
of all wavelengths corresponding to the light input/output ports (P
(k)) but reflects lights of wavelengths other than the above
wavelengths on the light axis between (E0) and (F(1)) and a light
input/output port (P0) on the reflection light axis of (F0)
Inventors: |
Takano, Toshihiko; (Tokyo,
JP) ; Jinnai, Kuniaki; (Tokyo, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
18699795 |
Appl. No.: |
09/897389 |
Filed: |
July 3, 2001 |
Current U.S.
Class: |
385/24 |
Current CPC
Class: |
G02B 6/2938 20130101;
G02B 6/29367 20130101 |
Class at
Publication: |
385/24 |
International
Class: |
G02B 006/293 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 4, 2000 |
JP |
202244/00 |
Claims
What is claimed is:
1. An optical demultiplexer/multiplexer for wavelengths of (n),
obtained by improving an optical demultiplexer/multiplexer for
wavelengths of (n-1) comprising a filter unit in which, (n-2)
pieces of, provided that n is an integer of 4.ltoreq.n.ltoreq.9,
selective transmission/reflection optical filters (F(k)), in which
k is an integer of 1.about.(n-2), are disposed on a plane A and a
plane B arranged in parallel so as to be successionally connected
with reflecting light axes, an external light input/output port
(E(0)) disposed outside the filter unit and positioned on the
reflecting light axis of the selective transmission/reflection
optical filter F(1) and (n-1) pieces of light input/output ports
(P(k)), in which k is an integer of 1.about.(n-1), disposed on the
transmission light axes of the selective transmission/reflection
optical filters F(k) and on the reflecting light axis of F(n-2),
wherein the improvement is comprising a selective
transmission/reflection optical filter (F0) which transmits lights
of all wavelengths corresponding to the light input/output ports
(P(k)) but reflects lights of wavelengths other than the above
wavelengths on the light axis between the external light
input/output port (E0) and the selective transmission/reflection
optical filter (F(1)) and a light input/output port (P0) on the
reflection light axis of the selective transmission/reflection
optical filter (F0).
2. An optical demultiplexer/multiplexer according to claim 1, which
has a structure in which the filter unit is composed of a block
made of metal, ceramics, or plastics, the block has a space where a
light is to be passed and the selective transmission/reflection
optical filters (F(k)) are fixed on the surface of the block.
3. An optical demultiplexer/multiplexer according to claim 1,
wherein the selective transmission/reflection optical filter is a
dielectric multilayer filter.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an optical
demultiplexer/multiplex- er used for multiplexing or demultiplexing
a plurality of signal lights which are different in wavelength from
each other.
PRIOR ART OF THE INVENTION
[0002] There have been proposed various systems with regard to an
optical demultiplexer/multiplexer having the functions of
multiplexing a plurality of signal lights having different
wavelengths or conversely demultiplexing a plurality of multiplexed
signal lights to each wavelength component. As one of the
proposals, a system using a selective transmission/reflection
optical filter is known. FIG. 4 is an illustration showing an
example of an optical demultiplexer/multiplexer according to a
conventional system using a selective transmission/reflection
optical filter.
SUMMARY OF THE INVENTION
[0003] It is an object of the present invention to provide an
optical demultiplexer/multiplexer using a plurality of selective
transmission/reflection optical filters in combination, which curbs
a light beam diffusion by minimizing an optical path length.
[0004] It is another object of the present invention to provide an
optical demultiplexer/multiplexer having a structure which enables
to minimize the size of a device as a whole while maintaining a
high performance.
[0005] According to the present invention, there Is provided an
optical demultiplexer/multiplexer for wavelengths of (n), obtained
by improving an optical demultiplexer/multiplexer for wavelengths
of (n-1) comprising a filter unit in which, (n-2) pieces of,
provided that n is an integer of 4.ltoreq.n.ltoreq.9, selective
transmission/reflection optical filters (F(k) ), in which k is an
integer of 1.about.(n-2), are disposed on a plane A and a plane B
arranged in parallel so as to be successionally connected with
reflecting light axes, an external light input/output port (E(0))
disposed outside the filter unit and positioned on the reflecting
light axis of the selective transmission/reflection optical filter
F(1) and (n-1) pieces of light input/output ports (P(k)), in which
k is an integer of 1.about.(n-1), disposed on the transmission
light axes of the selective transmission/reflection optical filters
F(k) and on the reflecting light axis of F(n-2),
[0006] wherein the improvement is comprising a selective
transmission/reflection optical filter (F0) which transmits lights
of all wavelengths corresponding to the light input/output ports
(P(k)) but reflects lights of wavelengths other than the above
wavelengths on the light axis between the external light
input/output port (E0) and the selective transmission/reflection
optical filter (F(1)) and a light input/output port (P0) on the
reflection light axis of the selective transmission/reflection
optical filter (F0).
BRIEF DESCRIPTION OF DRAWINGS
[0007] FIG. 1 is a plane view showing an example of the optical
demultiplexer/multiplexer of the present invention
[0008] FIG. 2 is an illustration showing properties of the
selective transmission/reflection optical filters in Example 1.
[0009] FIG. 3 is a plane view showing an example of the optical
demultiplexer/multiplexer of the present invention.
[0010] FIG. 4 is a plane view showing an example of a conventional
optical demultiplexer/multiplexer.
DETAILED DESCRIPTION OF THE INVENTION
[0011] In the present invention, symbols in the drawings have the
following meanings; E0: external light input/output port,
F0.about.F3: selective transmission/reflection optical filter and
P0.about.P4: light input/output port.
[0012] A known dielectric multilayer filter is preferred as the
selective transmission/reflection optical filter in the present
invention. The dielectric multilayer filter is produced, for
example, by laminating low refractive index thin films (silicon
dioxide, etc.) and high refractive index thin films (titanium
dioxide, etc.) alternately so as to form several tens of laminated
layers. It is possible to obtain a desired short-wave pass filter
(SPF), a desired long-wave pass filter (LPF) or a desired band-pass
filter by controlling these laminated film layers precisely. The
dielectric multilayer filter reflects almost 100% of lights in a
reflection region and has a transmittance near to 100% in a
transmission region so that the dielectric multilayer filter is
remarkably preferred.
[0013] As a material for the filter unit, there can be used metals,
ceramics, plastics and the like. Preferred examples thereof include
brass, stainless steel, machinable ceramics, epoxy resins and the
like. The inside of the filter unit where a light is passed is
provided with a space. When a material which is transparent in a
wavelength region to be used such as quartz glass is used, an
external portion alone may be processed for use while the inside is
retained as it is.
EXAMPLE
[0014] The optical demultiplexer/multiplexer of the present
invention will be explained more in detail with reference to
Examples hereinafter.
[0015] The following examples are described for explaining
concretely, while these examples shall not limit embodiments of the
present invention and the scope of the invention.
Example 1
[0016] FIG. 1 is a plane view showing an optical
demultiplexer/multiplexer for four wavelengths, which is an example
of the present invention.
[0017] In FIG. 1, a filter unit (2) made of stainless steel is
fixed in the central portion of a box (1). In the filter unit (2),
a plane A and a plane B are arranged in parallel in its end
portions and selective transmission/reflection optical filters (F0,
F1 and F2) are closely mounted on the plane A or the plane B. A
space is provided in an inside portion of the filter unit where a
light is to be passed. The plane A and the plane B are inclined at
an angle of 10 degree to the sides of the box (1).
[0018] Light input/output ports (P1, P2 and P3) and an external
light input/output port (E0) are positioned on transmission light
axes of the selective transmission/reflection optical filters so as
to correspond to the fixed positions of the selective
transmission/reflection optical filters and fixed to the box (1)
i.e. both outer sides of the filter unit (2). A light input/output
port (P0) is positioned on the reflection light axis of the
selective transmission/reflection optical filter and fixed to the
box (1). These light input/output ports are composed of an optical
fiber and a collimator lens attached to its end portion, while the
optical fiber and the collimator lens are not shown in FIG. 1.
[0019] A case in which a light prepared by multiplexing four kinds
of wavelengths (.lambda.1, .lambda.2, .lambda.3 and .lambda.4,
provided that .lambda.1<.lambda.2<.lambda.3<.lambda.4) is
entered from an external light input/output port (E0) will be
explained as an example.
[0020] Each of selective transmission/reflection optical filters
(F0, F1 and F2) has properties shown in FIG. 2. A light entered
from outside is led to a selective transmission/reflection optical
filter F0 (SPF) fixed on a plane A, a light of wavelength .lambda.4
is reflected with the selective transmission/reflection optical
filter F0, and the reflected light is led to a light input/output
port (P0). The resultant light (.lambda.1+.lambda.2+.lambda.3)
transmitted through the selective transmission/reflection optical
filter F0 is led to a selective transmission/reflection optical
filter F1 (SPF) fixed on a plane B, a light of wavelength .lambda.1
is transmitted through the selective transmission/reflection
optical filter F1, and the transmitted light is led to a light
input/output port (P1).
[0021] The reflected light (.lambda.2+.lambda.3) from the selective
transmission/reflection optical filter F1 is led to a selective
transmission/reflection optical filter F2 (SPF) fixed on the plane
A, a light of wavelength .lambda.2 is transmitted through the
selective transmission/reflection optical filter F2 and the
transmitted light is led to a light input/output port (P2). The
reflected light (.lambda.3) from F2 passes through the plane B and
reaches to a light input/output port (P3). In this way, the lights
of four kinds of wavelengths .lambda.1, .lambda.2, .lambda.3 and
.lambda.4 are demultiplexed to the light input/output ports of P0,
P1, P2 and P3 respectively.
[0022] When a light-travelling direction is adverse, this device
works as a multiplexer.
[0023] As a concrete combination of wavelengths, a combination of
wavelengths of .lambda.1: 1,515 nm, .lambda.2: 1,535 nm, .lambda.3:
1,555 nm and .lambda.4: 1,575 nm was used to prepare an optical
demultiplexer/multiplexer. Each wavelength light was entered from
E0 and measured at each port. In this case, there were obtained
fine results of the maximum insertion loss of .gtoreq.-1.5 dB and
an isolation of .ltoreq.-20 dB.
[0024] The characteristic features of the present invention exist
in that the selective transmission/reflection optical filter (F0)
and the light input/output port (P0) are provided before the light
from the external light input/output port (E0) reaches to the
selective transmission/reflection optical filter (F1).
[0025] According to the above structure, the sum total of optical
path lengths to the number of wavelengths to be multiplexed or
demultiplexed can be shortened. As a result, the diffusion of a
light beam is curbed to a minimum so that fine properties can be
obtained. Further, another advantage is that the size of a device
can be reduced to a width (W) as a minimum due to a rational layout
design.
[0026] Example 1 shows an example of a combination of SPFs
(short-wave pass filters), while the similar functions can be
attained by using LPFs (long-wave pass filters) or BPFs (band-pass
filters). For demultiplexing or multiplexing lights of n kinds of
wavelengths, at least (n-1) pieces of selective
transmission/reflection optical filters are required. For the
purpose of improving isolation or the like, it is also effective to
further add a selective transmission/reflection optical filter
before the light input/output ports (P(k)).
[0027] In the structure of the present invention, the upper limit
of the number of wavelengths which can be demultiplexed or
multiplexed depends upon properties of a selective
transmission/reflection optical filter to be used and a margin of a
system so that it can not be argued simply. However, it is
generally assumed that the limit of the number of wavelengths is
about 9 for attaining a preferable demultiplexing/multiple- xing
performance.
[0028] No special limitation is imposed on the angle of incidence
From the external light input/output port to the plane A of the
optical filter unit. However, it is preferred to select an angle of
15 degree or less as an inclined incident angle in view of filter
properties.
Example 2
[0029] FIG. 3 is a plane view of an optical
demultiplexer/multiplexer for four wavelengths in Example 2.
[0030] In the present example, part of the plane A of the filter
unit in Example 1 is inclined in the opposite direction at an angle
of 10 degree to the sides of the box, as shown in FIG. 3. In this
form, a light input/output port (P0) is provided at the side
opposite to the side of the other light input/output ports from a
straight line of from the external light input/output port (E0) to
F1.
[0031] The system of demultiplexing and multiplexing is the same as
that of Example 1. However, the form of the present example is
effective when it is difficult as a layout problem of the inside of
the box to dispose the light input/output port (P0) by using the
form of Example 1.
Effect of the Invention
[0032] As is evident from Examples and Detailed Description of the
Invention, the optical demultiplexer/multiplexer of the present
invention is remarkably high-performance and is compact so that it
can be preferably used for a WDM transmission device and the
like.
* * * * *